diff --git a/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php b/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php
index 53c09507aa..50c78f6ecb 100644
--- a/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php
+++ b/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php
@@ -593,7 +593,7 @@ final class PhabricatorApplicationTransactionCommentView
     // Merge options into groups.
     $groups = array();
     foreach ($action_map as $key => $item) {
-      $group_key = $item['groupKey'];
+      $group_key = $item['groupKey'] ?? '';
       if (!isset($groups[$group_key])) {
         $groups[$group_key] = array();
       }